This invention pertains to a system for providing consistent lubricant and/or gas flow through multiple permeable perimeter walls in a metal casting mold table.
Metal ingots and billets are typically formed by a casting process, which utilizes a vertically oriented mold situated above a large casting pit beneath the floor level of the metal casting facility. The lower component of the vertical casting mold is a starting block mounted on starting block pedestals. When the casting process begins, the starting blocks are in their upward-most position and in the molds. As molten non-ferrous metal is poured into the mold and cooled, the starting block is slowly lowered at a pre-determined rate by a hydraulic cylinder or other device. As the starting block is lowered, solidified non-ferrous metal or aluminum emerges from the bottom of the mold and ingots or billets are formed.
While the invention applies to casting of metals in general, including without limitations aluminum, brass, lead, zinc, magnesium, copper, steel, etc., the examples given and preferred embodiment disclosed are for aluminum, and therefore the term aluminum will be used throughout for consistency even though the invention applies more generally to metals.
While there are numerous ways to achieve and configure a vertical casting arrangement, FIG. 1 illustrates one example. In FIG. 1, the vertical casting of aluminum generally occurs beneath the elevation level of the factory floor in a casting pit. Directly beneath the casting pit floor 1a is a caisson 3, in which the hydraulic cylinder barrel 2 for the hydraulic cylinder is placed.
As shown in FIG. 1, the components of the lower portion of a typical vertical aluminum casting apparatus, shown within a casting pit 1 and a caisson 3, are a hydraulic cylinder barrel 2, a ram 6, a mounting base housing 5, a platen 7 and a starting block base 8, all shown at elevations below the casting facility floor 4.
The mounting base housing 5 is mounted to the floor 1a of the casting pit 1, below which is the caisson 3. The caisson 3 is defined by its side walls 3b and its floor 3a. 
A typical mold table assembly 10 is also shown in FIG. 1, which can be tilted as shown by hydraulic cylinder 11 pushing mold table tilt arm 10a such that it pivots about point 12 and thereby raises and rotates the main casting frame assembly, as shown in FIG. 1. There are also mold table carriages which allow the mold table assemblies to be moved to and from the casting position above the casting pit.
FIG. 1 further shows the platen 7 and starting block base 8 partially descended into the casting pit 1 with billet 13 being partially formed. Billet 13 is on starting block 14, which is mounted on pedestal 15. While the term starting block is used for item 14, it should be noted that the terms bottom block and starting head are also used in the industry to refer to item 14, bottom block typically used when an ingot is being cast and starting head when a billet is being cast.
While the starting block base 8 in FIG. 1 only shows one starting block 14 and pedestal 15, there are typically several of each mounted on each starting block base, which simultaneously cast billets or ingots as the starting block is lowered during the casting process.
When hydraulic fluid is introduced into the hydraulic cylinder at sufficient pressure, the ram 6, and consequently the starting block base 8, are raised to the desired elevation start level for the casting process, which is when the starting blocks are within the mold table assembly 10.
The lowering of the starting block base 8 is accomplished by metering the hydraulic fluid from the cylinder at a pre-determined rate, thereby lowering the ram 6 and consequently the starting blocks at a pre-determined and controlled rate. The mold is controllably cooled during the process to assist in the solidification of the emerging ingots or billets, typically using water cooling means.
There are numerous mold and pour technologies that fit into these mold tables. Some are generally referred to as xe2x80x9chot topxe2x80x9d technology, while others are more conventional casting technologies that use floats and downspouts, both of which are known to those of ordinary skill in the art. The hot top technology generally includes a refractory system and molten metal trough system located on top of the mold table, whereas the conventional pour technology involves suspending or supporting the source of molten metal above the mold table and the utilization of down spouts or tubes and floats to maintain the level of molten metal in the molds while also providing molten metal to the molds.
These different casting technologies have different advantages and disadvantages and produce various billet qualities, but no one of which is required to practice this invention.
The metal distribution system is also an important part of the casting system. In the two technology examples given, the hot top distribution trough sits atop the mold table while the conventional pouring trough is suspended above the mold table to distribute the molten metal to the molds.
Mold tables come in all sizes and configurations because there are numerous and differently sized and configured casting pits over which mold table are placed. The needs and requirements for a mold table to fit a particular application therefore depends on numerous factors, some of which include the dimensions of the casting pit, the location(s) of the sources of water and the practices of the entity operating the pit.
The upper side of the typical mold table operatively connects to, or interacts with, the metal distribution system. The typical mold table also operatively connects to the molds which it houses.
The use of a permeable or porous perimeter wall has proven to be an effective and efficient way to distribute lubricant and gas to the inside surface of a continuous casting mold, such as is described in U.S. Pat. No. 4,598,763 to Wagstaff.
In the typical use of a permeable perimeter wall, lubricant and gas are delivered to the perimeter wall under pressure through grooves or delivery conduits around the perimeter wall, typically using one delivery conduit (if grooves are used for the delivery of lubricant) and one or two delivery conduits (grooves) for the delivery of gas. The preferred lubricants are synthetic oils, whereas the current preferred gas is air. The lubricant and gas then permeate through the perimeter wall and are delivered to the interior of the mold as part of the casting process.
The perimeter walls on existing mold tables each have delivery conduits to deliver the lubricant and/or gas, and the delivery conduits may be circumferential groove-shaped delivery conduits with the same depth and width, or they may be holes partially drilled through the perimeter walls, or any other delivery means for that matter. The typical perimeter wall has a separate lubricant delivery conduit and a gas conduit.
Graphite has proven to be the preferred permeable material for use as the perimeter wall material or media. However, graphite has proven to be expensive in consistently producing high quality individual products which have very similar permeability to other graphite perimeter walls.
One of the significant factors causing the high cost incurred in providing consistent permeability or lubricant/gas flow rates through the perimeter walls is the variability in the relevant properties of the perimeter wall material. The properties related to the lubricant and gas flow rates can vary significantly from batch to batch of graphite for instance, and even within the same batch and within a given perimeter wall. Variations in properties such as porosity, permeability and density, impact the rate of delivery of lubricant and or gas through the perimeter wall. Furthermore, the viscosity of a particular lubricant or gas as well as the pressure at which the lubricant or gas is supplied to the perimeter wall, are factors affecting the respective flow rates through the permeable perimeter walls.
Experience has taught that graphite from a particular supplier or source will tend to have more similar properties than graphite from two different sources or suppliers, however, there may still be unacceptable variations in the properties of the graphite from a single source and even from a single batch. This is the case even though a particular density is typically specified when ordering.
In a typical application, one perimeter wall is used for each mold, and there are typically numerous molds on a single mold table, each mold having a perimeter wall. It is preferred to supply gas from one source line at one pressure and to supply lubricant from one source line at one pressure, to all perimeter walls in molds of a particular mold table.
The variations of most concern in the lubricant and/or gas flow rates through the graphite are therefore based on the variability in the properties of the graphite related to the respective flow rates, which becomes the critical factor in accomplishing the goal of the equal or predictable flow rates of lubricant and gas through the perimeter walls in each of the molds on the same mold table, or even in the same manufacturing facility.
Prior to this invention, achieving the same flow rate or delivery rate of lubricant and/or gas flow through multiple perimeter walls on the same mold table, was very time consuming and expensive, and resulted in significant waste. Each individual perimeter wall was extensively tested to determine its properties relevant to flow rate and an unnecessarily large percentage were rejected due to the flow rate variations.
With numerous molds on the same table simultaneously casting metal, it becomes critical to achieving a reliable process for producing high quality molded products (billet, ingot or special shapes) that the lubricant and/or gas delivered to the perimeter walls during casting is very closely the same from perimeter wall to perimeter wall in the same mold table.
In order to achieve consistent lubricant and/or gas flow rates through the perimeter walls in each of the molds in a given mold table, a high rate of rejection of graphite rings has been experienced. Typically, graphite perimeter walls with similar properties may be grouped together to achieve closely similar lubricant and/or gas flow rates. However, while grouping perimeter walls together may work for new construction, managing the selective replacement of perimeter walls in place in a facility can be very difficult.
From a practical and expense perspective, lubricant and/or gas are supplied at a constant pressure, and the perimeter walls are manufactured at a constant or fixed thickness and general size to fit within the molds. The inner and outer diameters of the perimeter walls, as well as their overall height also is generally fixed.
It is an objective of this invention to achieve a sufficiently consistent lubricant and/or gas flow rate through multiple perimeter walls on a mold table or in a casting facility, even though the perimeter walls generally have variations in their individual properties related to the flow rate of lubricant and/or gas through the perimeter wall body.
It is also an objective of this invention to reduce the significant expense of a high rejection rate for perimeter walls to achieve the sufficiently consistent lubricant and/or gas flow rate.
This invention accomplishes these objectives by providing a system for providing consistent lubricant and/or gas flow through multiple permeable perimeter walls. The system involves ascertaining one or more of the relevant properties, or the actual flow rate, of the perimeter walls, and then determining and creating the appropriate surface area of the delivery conduit which provides the lubricant and/or gas to the exterior of the perimeter wall, and/or the appropriate delivery distance.
The system provided by this invention has the significant advantage of allowing the use of multiple perimeter walls with different flow related properties, or with different lubricant and/or gas flow rates, to be used in the same mold table, while achieving consistent flow rates through each perimeter wall.
The system provided by this invention has the significant advantage of providing a significantly similar flow rate of lubricant or gas in a plurality of perimeter walls in molds on the same mold table.
In accomplishing these objectives, this invention provides a system which is simpler and less expensive than all prior systems.